A solid state disk (SSD), also called a solid state drive, is a hard disk made of a solid-state electronic storage chip array. SSDs are widely used in fields such as military, vehicles, industrial control, video surveillance, network monitoring, network terminals, electricity, medical care, aviation, and navigation devices. On the market, common SSD capacities usually include 60/64 gigabytes (GB), 120/128 GB, 240/256 GB, 480/512 GB, and 960/1024 GB. A value on the left of a slash represents a capacity available to a user, whereas a value on the right of a slash represents a physical space capacity of an SSD. A difference between the two values is called an over provisioning (OP) space. Usually, a user cannot perform an operation in the OP space, and a capacity of the OP space is usually determined by a primary controller. OP is generally used for performing an optimization operation, which includes wear balancing, garbage collection, bad block mapping, etc. An over provisioning ratio is a ratio of an over provisioning space capacity to the user available space capability, and over provisioning ratios in the industry are typically 7% and 28%. A physical space capacity of 1024 GB is used as an example. When a user available space capacity is 960 GB, a corresponding over provisioning ratio is 7%, namely, (1024−960)/960=7%. When a user available space capacity is 800 GB, a corresponding over provisioning ratio is 28%, namely, (1024−800)/800=28%. A larger over provisioning ratio corresponds to a better random write performance, a smaller performance fluctuation, and a longer service life. However, higher OP ratio means higher cost.
A flash memory in the SSD needs to be erased before being rewritten. Writing and reading are in pages while erasing is in blocks. Therefore, a volume of actually written data is much greater than that of data written by a host. Write amplification (WA) is a ratio of a volume of actually written data to a size of data written by a host. Larger WA corresponds to a smaller over provisioning ratio, a shorter service life, and poorer random write performance.
Currently, an SSD vendor provides multiple over provisioning ratios for an SSD of a specific capacity, and a user selects a fixed over provisioning ratio according to a user requirement. Once an over provisioning ratio is fixed, parameters of the SSD are fixed, and performance and a service life of the SDD are also fixed. In this way, the SSD can only run at the fixed over provisioning ratio. Consequently, it is difficult to further optimize the performance and the service life of the SSD.